Electrical overstress event indicator on electronic circuitry

ABSTRACT

Detecting electrical overstress events in electronic circuitry such as optical emitters. In one example embodiment, a laser includes an active area and a contact region in electrical communication with the active area. A portion of the contact region is configured to manifest a change in a visual attribute of the portion in response to exposure of the portion to an electrical overstress event.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Patent ApplicationSer. No. 60/809,667, filed on May 31, 2006, which is incorporated hereinby reference in its entirety.

BACKGROUND

1. The Field of the Invention

The present invention relates to detecting malfunctions in electroniccircuitry. More particularly, embodiments of the invention relate todetecting electrical overstress events in electronic circuitry such asoptical emitters.

2. Related Technology

Electronic circuitry is increasingly integrated into data communicationand data processing devices. For example, integrated circuits, oftenreferred to as a microchips or simply chips, are used in a variety ofapplications, such as high speed optical networks. One type of chip, thelaser diode chip, plays an increasingly important role in modern highspeed optical networks. Laser diode chips are complex semiconductordevices that convert an electrical data signal into an optical datasignal. A laser diode chip, also known simply as a laser, is anessential component of a transmitter optical sub assembly (TOSA). A TOSAis often paired with a receiver optical sub assembly (ROSA) in anoptoelectronic transceiver.

Examples of lasers that can be integrated into optoelectronictransceivers include vertical cavity surface emitting lasers (VCSELs)and edge emitting lasers. While VCSELs and edge emitting lasers exhibitdesirable performance characteristics, they also have the unfortunatedrawback of being very susceptible to electrical overstress (EOS)events. EOS events include events that can cause failure in a laser andare characterized by exposure of the laser to excessive voltage,current, and/or power. An electrostatic discharge (ESD) event is aparticular type of EOS event where a rapid transfer of electrostaticcharge occurs between two objects. EOS events, and ESD events inparticular, can damage a laser in many ways, often resulting inobservable signs of damage or failure attributes.

EOS damage is not always obvious though. In fact, some EOS events damagea laser without leaving any apparent visible manifestation of thedamage. Such EOS events can still render the laser non-functional, evenif no physical anomalies are visibly evident. Less damaging EOS eventsmay also occur. Although these less damaging EOS events may not renderthe laser non-functional, these EOS events can shift the parametricperformance of the laser, thus causing the laser to produce aninaccurate optical data signal.

Often when an optoelectronic transceiver containing a malfunctionallaser is returned by a customer, it becomes necessary for themanufacturer to determine what caused the laser to malfunction. Forexample, it may be necessary for the manufacturer of a particularoptoelectronic transceiver to make a determination as to whether thelaser of the optoelectronic transceiver malfunctioned due to an ESDevent, or whether the laser malfunctioned due to some other cause, suchas a growth defect in the laser. Where there is no apparent visiblemanifestation of on a laser surface, the processes of performing afailure analysis on the laser can be very costly in terms of time andexpense.

It would therefore be useful to be able to readily detect the occurrenceof an EOS event which caused a particular laser to malfunction in orderto save the time and expense of performing a failure analysis on thelaser.

BRIEF SUMMARY OF SOME EXAMPLE EMBODIMENTS

In general, example embodiments of the invention relate to detectingelectrical overstress events in electronic circuitry such as opticalemitters. Some example embodiments of the invention can provide a visualcue to anyone inspecting a laser that an electrical overstress (EOS)event has occurred.

In one example embodiment, a laser includes an active area and a contactregion in electrical communication with the active area. A portion ofthe contact region is configured to manifest a change in a visualattribute of the portion in response to exposure of the portion to anelectrical overstress event.

In another example embodiment, a laser includes an active area, acontact region in electrical communication with the active area, and asacrificial element. The sacrificial element and the contact region areelectrically connected to the active area. The sacrificial element isalso configured to be visibly altered in response to exposure of thecontact region to an electrical overstress event.

In yet another example embodiment, a laser includes an active area, acontact region in electrical communication with the active area, and ameans for visibly manifesting exposure of the contact region to anelectrical overstress event.

In another example embodiment, an optoelectronic transceiver includes ahousing, a ROSA at least partially positioned within the housing, and aTOSA at least partially positioned within the housing. The TOSA includesa laser. The laser includes an active area, a contact region inelectrical communication with the active area, and a means for visiblymanifesting exposure of the contact region to an electrical overstressevent.

These and other aspects of example embodiments of the present inventionwill become more fully apparent from the following description andappended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

To further clarify the above and other aspects of example embodiments ofthe present invention, a more particular description of these exampleswill be rendered by reference to specific embodiments thereof which aredisclosed in the appended drawings. It is appreciated that thesedrawings depict only example embodiments of the invention and aretherefore not to be considered limiting of its scope. It is alsoappreciated that the drawings are diagrammatic and schematicrepresentations of example embodiments of the invention, and are notlimiting of the present invention nor are they necessarily drawn toscale. Example embodiments of the invention will be disclosed andexplained with additional specificity and detail through the use of theaccompanying drawings in which:

FIG. 1 is a perspective view of an optoelectronic transceiver modulethat serves as one example environment in which example embodiments ofthe present invention can be practiced;

FIG. 2 discloses aspects of an example optical emitter, such as avertical cavity surface emitting laser (VCSEL); and

FIG. 3 discloses aspects of another example optical emitter, such as aVCSEL.

DETAILED DESCRIPTION OF SOME EXAMPLE EMBODIMENTS

Example embodiments of the present invention enable the visual detectionof the occurrence of electrical overstress (EOS) events in electroniccircuitry. For example, embodiments of the invention can be lasers, suchas vertical cavity surface emitting lasers (VCSELs). A laser can beintegrated into various optical components including transmitter opticalsub assemblies (TOSAs). A TOSA can be integrated together with areceiver optical sub assembly (ROSA) in the housing of an optoelectronictransceiver.

1. Example Optoelectronic Transceiver Module

Reference is first made to FIG. 1, which is a perspective view of anexample optoelectronic transceiver module (“transceiver”), generallydesignated at 100, for use in transmitting and receiving optical signalsin connection with an external host device (not shown). As disclosed inFIG. 1, the transceiver 100 includes various components, including areceiver optical subassembly (“ROSA”) 102, a transmitter opticalsubassembly (“TOSA”) 104, electrical interfaces 106 and 108, variouselectronic components 110, and a printed circuit board (“PCB”) 112. Indetail, the two electrical interfaces 106 and 108 electrically connectthe ROSA 102 and the TOSA 104, respectively, to a plurality ofconductive pads located on the PCB 112. As disclosed in connection withthe ROSA 102, the electrical interface 106 is connected to a group ofmetal posts 113 which are electrically connected to an optical receiver(not shown) housed within the ROSA 102. Although not disclosed in FIG.1, the electrical interface 108 could be similarly connected to metalposts (not shown) of the TOSA 104 which are electrically connected to anoptical transmitter (not shown) housed within the TOSA 104.

The electronic components 110 are also operably attached to the PCB 112.An edge connector 114 is located on an end of the PCB 112 to enable thetransceiver 100 to electrically interface with a host device (notshown). As such, the PCB 112 facilitates electrical communicationbetween the ROSA 102/TOSA 104 and the host device. In addition, theabove-mentioned components of the transceiver 100 are partially housedwithin a shell 116. The shell 116 can cooperate with a covering portion(not shown) to define a housing for the components of the transceiver100.

The transceiver 100 can be configured for optical signal transmissionand reception at a variety of per-second data rates including, but notlimited to, 1 Gbit, 2 Gbit, 2.5 Gbit, 4 Gbit, 8 Gbit, 10 Gbit, 10.3Gbit, 10.5 Gbit, or higher. Further, the transceiver 100 can beconfigured for optical signal transmission and reception at variouswavelengths including, but not limited to, 850 nm, 1310 nm, 1470 nm,1490 nm, 1510 nm, 1530 nm, 1550 nm, 1570 nm, 1590 nm, or 1610 nm. Also,the transceiver 100 can be configured to support various communicationprotocols including, but not limited to, Fast Ethernet, GigabitEthernet, 10 Gigabit Ethernet, and 1×, 2×, 4×, and 10× Fibre Channel.Further, the transceiver 100 can be configured to operate at varioustemperature ranges including, but not limited to, 0° C. to 70° C. Inaddition, the transceiver 100 can be configured to have a variety ofdifferent form factors that are substantially compliant with varioustransceiver and/or transponder MSAs including, but not limited to, SFF,SFP, XFP, XPAK, X2, or XENPAK.

With continued reference to FIG. 1, the TOSA 104 includes a barrel 118within which an optical transmitter, such as a laser (not shown), ispositioned. The optical transmitter is configured to convert electricalsignals received through the PCB 112 from a host device (not shown) intocorresponding optical signals. Accordingly, the TOSA 104 serves as anelectro-optic transducer. The TOSA 104 also defines a port (not shown).The port is configured to optically connect the optical transmitterpositioned within the barrel 118 with the fiber-ferrule portion of anoptical fiber connector (not shown).

Having described a specific environment with respect to FIG. 1, it willbe understood that this specific environment is only one of countlessarchitectures in which example embodiments of the present invention maybe employed. As previously stated, example embodiments of the presentinvention are not intended to be limited to any particular environment.

2. Example Optical Emitters

FIG. 2 is a top view of an example VCSEL 200 that is configuredaccording to one example embodiment of the present invention. The VCSEL200 is typically fabricated on a semiconductor wafer along with hundredsor thousands of other VCSELs. The VCSEL 200 includes an active area 202through which laser light is emitted in a direction perpendicular to theactive area 202. The VCSEL 200 also includes a generally round contactregion 204 which connects, in this example embodiment, to a generallyrectangular contact region 206. The contact regions 204 and 206 are inelectrical communication with the active area 202. In particular,current is injected into the VCSEL 200 through the contact regions 204and 206 in order to provide electrical power to the VCSEL 200. Light isthen emitted from the VCSEL 200 as a result of the current injection. Inthe example VCSEL 200 of FIG. 2, the contact regions 204 and 206comprise an electrically conductive material, such as a metal or a metalalloy.

In addition, one or both of the contact regions 204 and 206 alsoincorporate a means for visibly manifesting exposure of the contactregions 204 and/or 206 to an EOS event. The means for visiblymanifesting exposure to an EOS event can generally include multiplemeans. In one example embodiment, the means for visibly manifestingexposure to an EOS event in the VCSEL 200 is implemented as a chemicalor polymer configured to change color, texture, or other visiblyperceptible characteristic upon exposure to an EOS event.

For example, the metal from which the contact regions 204 and 206 arefabricated could be coated with, or otherwise include, a chemical orpolymer which causes the metal to change color upon the exposure of themetal to an EOS event. In one example, if the expected EOS event is anelectrostatic discharge (ESD) event, contact regions 204 and/or 206 canbe coated with an ESD-sensitive paint. The ESD-sensitive paint can, forexample, include nano-crystals that are configured to change directionsuch that the nano-crystals are substantially oriented along thedischarge path of the ESD event. This change of orientation can resultin a change of color from, for example, bright gold to dark red. TheESD-sensitive paint could be similar to a thermal-indicating paint thatis configured to change color at a given temperature. In this example,the appearance of a dark red path along the surface of contact regions204 and/or 206 would indicate both that an ESD event had occurred, andwould also identify at least a portion of the discharge path associatedwith the ESD event.

An example discharge path beginning at the active area 202 and extendingacross the contact regions 204 and 206 is indicated generally in FIG. 2as a discharge path 208. In this example, prior to the occurrence of theESD event, the contact regions 204 and 206 appeared to be bright gold incolor, but subsequent to the ESD event, the discharge path 208 acrossthe contact regions 204 and 206 turned dark red in color while theremainder of the contact regions 204 and 206 remained bright gold incolor. The colors bright gold and dark red are examples only, and anyother color combination could be substituted in the above example.Likewise, a change in color contrast or brightness, such as where acolor becomes lighter or darker, could also be substituted in the aboveexample.

Alternatively, the metal from which the contact regions 204 and 206 arefabricated could be coated with, or otherwise include, a chemical orpolymer which causes the metal to change texture upon the exposure ofthe metal to an ESD event. For example, the texture of the metal couldchange from being smooth and reflective to being rough and dull upon theexposure of the metal to an ESD event. In this example, the exampledischarge path 208 would appear smooth and shiny in texture prior to theoccurrence of an ESD event, but subsequent to the occurrence of the ESDevent, the discharge path 208 would appear rough and dull in texture.This alternative configuration would indicate both that an ESD event hadoccurred, and would also identify at least a portion of the dischargepath associated with the ESD event. The smooth and rough textures areexamples only, and any other texture, or combination, could besubstituted in the above example.

In general, anything that visually distinguishes the EDS affectedportion of a device from unaffected portions can be employed and thescope of the invention is not limited to the disclosed examples.

Likewise, a combination of visibly perceptible characteristics, such ascolor and texture, can be used to visibly indicate the occurrence of anEOS event. Furthermore, any electrically conductive material that iselectrically connected to a laser can be configured to change color,texture, or other visibly perceptible characteristic upon exposure to anEOS event, as disclosed herein. For example, where a VCSEL isimplemented in a fiber optics system and positioned inside a housing ofa TOSA, such as the housing 118 of the TOSA 204, one or more metal postsof the TOSA can include the chemical/polymer which functions asdisclosed herein. A change in appearance of one or more of the metalposts of the TOSA 204 according to this configuration would indicateboth that an EOS event has occurred, and would also identify at least aportion of the discharge path associated with the EOS event.

In each of the above examples, the occurrence and discharge path of anEOS event can be detected by a visual inspection of one or more surfacesof the VCSEL 200 or associated electrically conductive material that iselectrically connected to the VCSEL 200. This visual inspection can beperformed in some circumstances with the assistance of a surfaceinspection instrument such as, for example, a scanning electronmicroscope. Even where the occurrence of an EOS event does not result incatastrophic failure of the VCSEL 200, the example embodiment of FIG. 2provides a visual cue, to anyone inspecting the VCSEL 200 and/or relatedcomponents such as the metal posts of the TOSA discussed above, that anEOS event had occurred. Knowledge that an EOS event has occurred canthen be used in deciding what remedial actions may need to be taken inorder to insure proper functioning of the component into which the VCSEL200 is integrated, in deciding how to compensate a customer whopurchased the component for any malfunction of the component, or indeciding how to alter the design of the VCSEL 200 and/or the VCSEL 200production process.

FIG. 3 is a top view of an example VCSEL 300 that is configuredaccording to another example embodiment of the present invention. TheVCSEL 300 can be fabricated on a wafer in a similar manner as the VCSEL200 of FIG. 2. Also similar to the VCSEL 200, the VCSEL 300 includes anactive area 302 and contact regions 304 and 306. In addition, the VCSEL300 includes a means for visibly manifesting exposure of the contactregions 304 and/or 306 to an EOS event.

The means for visibly manifesting exposure of the contact regions 304and/or 306 in the VCSEL 300 is a sacrificial element whose only purposeis to be visibly altered in response to the occurrence of an EOS event.The example sacrificial element illustrated in FIG. 3 is a resistorcircuit 308. The resistor circuit 308 and the contact region 306 areelectrically connected in parallel with respect to the active area 302.The resistor circuit 308 is configured to visibly burn out when an EOSevent occurs in the vicinity of the contact region 306. The term “burnout” in this context refers to the destruction of a sacrificial elementfrom excessive current or power dissipation such as occurs as a resultof an EOS event. When the resistor circuit 308 burns out, the resistorcircuit 308 will change in appearance due to one or more ofcarbonization of plastic around the resistor circuit 308, metal reflowaround the resistor circuit 308, and/or discoloration of the metalaround the resistor circuit 308. The resistor circuit 308 is only oneexample of a sacrificial element, and the resistor circuit 308 can bereplaced with any other sacrificial element or elements of comparablefunctionality including more complex circuits containing any combinationof circuit elements, for example, capacitors and/or diodes.

Since the resistor circuit 308 is located adjacent to the contact region306, when an EOS event occurs in the vicinity of the contact region 306,the resistor circuit 308 will burn out and the appearance of theresistor circuit 308 will visibly indicate that an EOS event hasoccurred along the contact region 306 of the VCSEL 300. Therefore, inthe example embodiment of FIG. 3, the occurrence and approximatedischarge path of an EOS event on the VCSEL 300 can be detected visuallyby inspecting the resistor circuit 308. The VCSEL 300 could includemultiple resistor circuits similar to the resistor circuit 308, or othersimilar sacrificial elements of comparable functionality, in order toenable further detection and pinpointing of the occurrence of EOSevents. As the foregoing makes clear, resistor circuits and otherdevices and systems of comparable functionality, comprise yet furtherexample structural implementations of a means for visibly manifestingexposure to an EOS event. Any other structural implements of comparablefunctionality may additionally, or alternatively, be employed. Inaddition, variables such as size of resistor can be adjusted to suitapplication requirements.

Even where the occurrence of an EOS event does not result incatastrophic damage to the VCSEL 300, the example embodiment of FIG. 3provides a visual cue, to anyone inspecting the VCSEL 300, that an EOSevent had occurred. Likewise, where the resistor circuit 308 isconfigured to burn out at the same time that the VCSEL 300 fails, it caneasily be determined by visually examining the resistor circuit 308whether the cause of failure of the VCSEL 300 was due to an EOS event ordue to some other cause, such as a growth defect. For example, when theVCSEL 300 fails, the resistor circuit 308 can be examined. If anexamination of the resistor circuit 308 reveals that the resistorcircuit 308 has burned out, then it can be determined that an EOS eventwas the cause of the VCSEL 300 failure. On the other hand, if anexaminer of the resistor circuit 308 reveals that the resistor circuit308 has not burned out, then it can be determined that the failure ofthe VCSEL 300 was not caused by an EOS event.

Knowledge that an EOS event has occurred can then be used, for example,in deciding what remedial actions may need to be taken in order toinsure proper functioning of the component into which the VCSEL 300 isintegrated, in deciding how to compensate a customer who purchased thecomponent for any malfunction of the component, or in deciding how toalter the design of the VCSEL 300 and/or the VCSEL 300 productionprocess.

Although the examples disclosed herein relate generally to apparatusesthat enable detection of EOS events in lasers such as VCSELs, exampleembodiments of the invention are not limited to lasers or VCSELs, butextend instead to all electronic circuitry and other integrated circuitswhere the detection of EOS events would prove beneficial. Exampleembodiments of the invention also extend to any means for visiblymanifesting exposure to an EOS event, and are not limited to the examplemeans for visibly manifesting exposure to EOS events disclosed herein.

The present invention may be embodied in other specific forms withoutdeparting from its spirit or essential characteristics. The disclosedembodiments are to be considered in all respects only as illustrativeand not restrictive. The scope of the invention is, therefore, indicatedby the appended claims rather than by the foregoing description. Allchanges which come within the meaning and range of equivalency of theclaims are to be embraced within their scope.

1. A laser comprising: an active area; and a contact region inelectrical communication with the active area, a portion of the contactregion being configured to manifest a change in a visual attribute ofthe portion in response to exposure of the portion to an electricaloverstress event.
 2. The laser as recited in claim 1, wherein thecontact region is configured to manifest a change in a color of theportion of the contact region in response to exposure of the portion toan electrical overstress event.
 3. The laser as recited in claim 1,wherein the contact region is configured to manifest a change in atexture of the portion of the contact region in response to exposure ofthe portion to an electrical overstress event.
 4. The laser as recitedin claim 1, wherein the contact region is configured to manifest achange in a color contrast of the portion of the contact region inresponse to exposure of the portion to an electrical overstress event.5. The laser as recited in claim 1, wherein the contact region isconfigured to manifest a change in a color and a texture of the portionof the contact region in response to exposure of the portion to anelectrical overstress event.
 6. The laser as recited in claim 1, whereina second portion of the contact region is not configured to manifest achange in a visual attribute of the second portion in response toexposure of the second portion to an electrical overstress event.
 7. Thelaser as recited in claim 1, wherein the laser comprises a VCSEL.
 8. Anoptoelectronic transceiver comprising: a housing; a ROSA at leastpartially positioned within the housing; and a TOSA at least partiallypositioned within the housing and including the laser as recited inclaim
 1. 9. A laser comprising: an active area; a contact region inelectrical communication with the active area; and a sacrificial elementthat is electrically connected to the active area, the sacrificialelement being configured to be visibly altered in response to exposureof the contact region to an electrical overstress event.
 10. The laseras recited in claim 9, wherein the sacrificial element comprises aresistor circuit.
 11. The laser as recited in claim 10, wherein theresistor circuit is configured to change in appearance due tocarbonization of plastic around the resistor circuit in response toexposure of the contact region to an electrical overstress event. 12.The laser as recited in claim 10, wherein the resistor circuit isconfigured to change in appearance due to metal reflow around theresistor circuit in response to exposure of the contact region to anelectrical overstress event.
 13. The laser as recited in claim 10,wherein the resistor circuit is configured to change in appearance dueto discoloration of metal around the resistor circuit in response toexposure of the contact region to an electrical overstress event. 14.The laser as recited in claim 9, wherein the laser comprises a VCSEL.15. An optoelectronic transceiver comprising: a housing; a ROSA at leastpartially positioned within the housing; and a TOSA at least partiallypositioned within the housing and including the laser as recited inclaim
 9. 16. A laser comprising: an active area; a contact region inelectrical communication with the active area; and a means for visiblymanifesting exposure of the contact region to an electrical overstressevent.
 17. The laser as recited in claim 16, wherein the laser comprisesa VCSEL.
 18. An optoelectronic transceiver comprising: a housing; a ROSAat least partially positioned within the housing; and a TOSA at leastpartially positioned within the housing and including a laser, the lasercomprising: an active area; a contact region in electrical communicationwith the active area; and a means for visibly manifesting exposure ofthe contact region to an electrical overstress event.
 19. Theoptoelectronic transceiver as recited in claim 18, wherein the lasercomprises a VCSEL.
 20. The optoelectronic transceiver as recited inclaim 18, wherein the means for visibly manifesting exposure isconfigured to manifest a change in a color of a portion of the contactregion in response to exposure of the contact region to an electricaloverstress event.
 21. The optoelectronic transceiver as recited in claim18, wherein the means for visibly manifesting exposure is configured tomanifest a change in a texture of a portion of the contact region inresponse to exposure of the contact region to an electrical overstressevent.
 22. The optoelectronic transceiver as recited in claim 18,wherein the means for visibly manifesting exposure comprises asacrificial element that is configured to be visibly altered in responseto exposure of the contact region to an electrical overstress event. 23.The optoelectronic transceiver as recited in claim 22, wherein thesacrificial element comprises a resistor circuit.